Investigation of Measured Received Power from FM ...
Transcript of Investigation of Measured Received Power from FM ...
Journal of Information Engineering and Applications www.iiste.org
ISSN 2224-5782 (print) ISSN 2225-0506 (online)
Vol.4, No.12, 2014
10
Investigation of Measured Received Power from FM Broadcasting
Radios-A Case of Tanzania
Jan Kaaya Anael Sam
Nelson Mandela African Institution of Science and Technology (NM-AIST), School of Computational and
Communication Science and Engineering
Arusha, Tanzania
Email:[email protected] ;[email protected]
Abstract
Aeronautical ground to air Very High Frequency Communication (COM) systems is among communication
safety services in aircraft which safeguard life and property and is the main voice communication between pilots
of aircraft and control tower. These systems have been facing interference from Frequency Modulation (FM)
broadcasting radio stations. With increase in number of FM radio stations in Tanzania these interferences case
increases hence pause for immediate measure to mitigate interferences. This paper compares the received signal
level at Designated Operational Coverage of COM facilities with established minimum threshold level and there
after comparison of empirical radio propagation models against measured data. It was observed that the signal
level from FM broadcasting radios were strong enough to cause interference. Hence concluded corner reflector
antenna has to be used as interference mitigation technique so as to lower the FM broadcasting power level
reaching aeronautical communication facilities.
Keywords: FM, VHF, COM, propagation and Transmission Loss.
1. Introduction
As the number of FM broadcasting radio signal in Tanzania increase, interference cases to Aeronautical VHF
ground to air communication have increased too [1]. Electromagnetic interference energy from FM broadcasting
stations reaches victim aeronautical systems receivers by two primary mechanisms which are radiation and
conduction [2]. Radiation have subdivided into two further categories which are direct radiation in which
interfering FM broadcasting transmitter radiates electromagnetic energy using the same frequency as the
interfered aeronautical communications system[3] and third order intermodulation products radiations in which
one or more strong interfering signals on certain frequencies related to the one which an aeronautical system is
operating cause interference effects to aeronautical communication systems. For induction electromagnetic
interfering energy from FM broadcasting transmitters get induced into aeronautical systems when the two
systems are placed close to each other hence Radio Frequency currents can be induced in its lengths [3, 4].
With consideration of importance and necessity of aeronautical communication facilities as safety
services with primary status compared to broadcasting services which fall under secondary status[5] mitigation
measures to alleviate interference are of prime importance.
2. Literature review
2.2.1 Third Order Intermodulation Products
FM broadcasting radio third order intermodulation products occur when two or more separate frequencies exist
together in a non-linear device hence sum and difference frequencies are also produced in addition to the
harmonics. Three types of intermodulation products which originates from FM broadcasting radio systems
include
� single channel intermodulation in which the wanted signal is distorted by virtue of non-linearity in the
transmitter
� inter transmitter intermodulation in which one or more transmitters on a same site produce
intermodulation products either within the transmitters themselves or within a non-linear component on
site to produce intermodulation products and
� intermodulation due to passive circuits: where transmitters share the same radiating element and
intermodulation occurs due to non-linearity’s of passive circuits [6].
Intermodulation also may get generated in aeronautical system receiver as a result of the receiver being driven
into non-linearity by high power from FM broadcasting signals outside the aeronautical band. For this
interference to occur two or more broadcasting signals which have frequency relationship which, in a non-linear
process, can produce an intermodulation product within the wanted RF channel in use by the aeronautical
receiver. [3].
Intermodulation products of two frequencies f1 and f2 and their orders of intermodulation products are shown in
Table 1:
Journal of Information Engineering and Applications www.iiste.org
ISSN 2224-5782 (print) ISSN 2225-0506 (online)
Vol.4, No.12, 2014
11
Table 1: Intermodulation products of two frequencies
Intermodulation Order Intermodulation
Products
Intermodulation
Products
1st Order f1 f2
2nd
Order f1+f2 f2-f1
3rd
Order 2f1+f2, 2f1-f2 2f2-f1, 2f2+f1
4th
Order 2f1+2f2 2f2-2f1
5th
Order 3f1-2f1, 3f1+2f2 3f2-2f1, 3f2+2f2
2.2.2 Protection Ratio
There are two established principles for protection of desired signal within Designated Operational Coverage
(DOC) of COM facilities;
i. The first principle calculates the actual field strength of desired and undesired signal at the COM
receiver antenna. On the basis of the established Desired to Undesired signal D/U ratio, the maximum
signal level of the undesired (interfering) signal determines in turn the maximum level of the interfering
signal, before the interference becomes harmful[7].
ii. The second principle uses the minimum field strength at the COM receiver antenna. The stipulated
protection ratio is between 14 to 20 dB between desired signal and undesired signal In this the standard
set for DOC is electric field strength of 75 dBµV which is equivalent to (-82 dBm). With consideration
of 20dB margin interfering has to be lower than -102dBm [8].
(1)
Where;
Pd= power of the undesired signal at the receiver (dBW)
Pu= power of the desired signal at the receiver (dBW)
D/U= Protection ratio (dB)
2.2.3 Radio Propagation Models
Propagation of radio waves involves mechanism such as reflection which occurs when radio wave propagation in
one medium impinges upon another medium with different electromagnetics properties, scattering when radio
waves hits a rough surface or an object which is having a size much smaller than the signal wave length and
diffraction which is caused by bending of propagating radio waves when encounter obstacles. VHF signal
propagate by using space waves when travelling from transmitter to the receiver[9].
Table 2: Frequencies Bands and propagation mode
Frequency Band Frequency Range Propagation Mode
Extremely Low Frequency Less than 3 KHz Ground wave
Very Low Frequency 3KHz-30 KHz Earth/ Ionosphere guided wave
Low Frequency 30KHz-300 KHz Ground wave
Medium Frequency 300KHz -3 MHz Ground and Sky wave
High Frequency 3MHz – 30 MHz Sky wave
Very High Frequency 30 MHz-300MHz Space wave
Ultra High Frequency 300 MHz- 3000MHz Space wave
Super High Frequency 3GHz-30 GHz Space wave
Extremely High Frequency 30 GHz – 300GHz Space wave
For prediction of propagation of radio signal in different terrain environments different radio
propagation modals have been developed. Radio propagation models are mathematical formulation which
characterises propagation of radio waves as a function of power, frequency, distance and other link
conditions[10]. These models are useful during planning of frequencies by communication regulators since assist
to predict coverage and probability of interference at a given distance from the transmitter.Henceforth prediction
of path loss is significant element in designing communication system[11]. A reliable propagation model
calculates the path loss with small standard deviation. Propagation models are divided into empirical and
deterministic models. [12] checked suitability of Free space propagation model, Hata Okumura path loss model,
Okumura model and Extended COST- 231 Hata for predicting propagation of FM broadcasting signals in North
India and concluded that Extended COST- 231 Hata Model was the best in predicting broadcasting signals. The
same result was obtained in hilly areas of Nigeria [13].
In this paper three empirical model which free space attenuation model, two ray reflection model and Egli model
have been discussed and compared against the measured data.
i. Free Space Path loss model
Free-space propagation model is used to predict received signal strength when the path between the transmitter
and the receiver is a clear and unobstructed line-of-sight[12]. The ideal antenna propagation radiates in all
Journal of Information Engineering and Applications www.iiste.org
ISSN 2224-5782 (print) ISSN 2225-0506 (online)
Vol.4, No.12, 2014
12
directions from transmitting source and propagating to an infinite distance with no degradation. Attenuation
occurs due to spreading of power over greater areas [4].
Henceforth the resulting power density Pd is calculated using equation
24
td
PP
dπ=
(2)
Where;
Pt is the transmitted power
Pd is power at distance d from antenna.
As the signal propagates from the antenna, it experiences a reduction in intensity and the amount of power
received depends on the effective capture area of the receiving antenna. The power received Pr for a given power
density is calculated as
r d eP P A= ×
(3)
Where Ae is the effective antenna aperture and is given by equation 2
4eA
λ
π=
(4)
Where
λ is the signal wavelength of propagated signal.
The amount of power captured by the antenna at the certain distance d, thus depends on power density and also
on the effective capture aperture of the antenna. Combining equations (1) and (3) into (2), we have the power
received to be as expressed as 2
4r tP P
d
λ
π
=
(5)
The free space path loss Lp is given as Pt / Pr and can represented in terms of frequency rather than wavelength
of signals, we can make the substitution λ= c/f to get the free space path loss as shown in equation 5 2
2 24L p d f
c
π =
(6)
Where
c and f are the speed of light and operating frequency respectively.
The free space path loss equation can be represented in logarithmic
10 1032.5 20 log 20 logLp d f= + +
(7)
Where by frequency f is in MHz and distance d in kilometre
In free space Electric field strength can be calculated by equation;
3 0 t t
f s
P GE
d=
(8)
Where
Efs = Electric field in free space
Pt= power transmitted
Gt= Gain of the transmitter
D = distance from transmitter
ii. Two Ray Ground Reflection Model
In this model the total received power at the receiver is taken to be summation of power from two different paths
which are direct path between transmitter and receiver second path is obtained by one ground reflection of the
signal wave in between transmitter and receiver. This model also considers the height of location of receiver &
Journal of Information Engineering and Applications www.iiste.org
ISSN 2224-5782 (print) ISSN 2225-0506 (online)
Vol.4, No.12, 2014
13
transmitter with respect to the ground[14].
Mathematical formula for calculating received power at a distance d, is given as: 2 2
4
t t r t rr
P G G h hP
d L=
(9)
Where;
Pr= Received power of the transmitter at distance d
Pt= Power transmitted by the transmitter
Gt= Gain of the transmitter
Gr= Gain of the receiver
ht= Height of the transmitter
hr= Height of the receiver
L= System loss
D= separation distance between transmitter and receiver
iii. Egli Model
Egli model also is among the empirical model which is used to predict propagation losses taking into account the
effect of the terrain, when both the transmitting and the receiving antenna are located relatively close to the
ground. This model gives more accurate prediction of path loss when compared to the free space model. The
Egli model is based on measured path losses and converted into the following mathematical model and provides
an alternative generic method to predict propagation losses when the antennas are close to the ground and
includes an empirical frequency dependent correction for frequencies greater than 30 MHz
Mathematically power received at the receiver antenna is given by equation:
40logD 20log 20log 20log40 20logr t t r r p t rP P G G L L H H f= + + − − − + + + −
(10)
Where;
Pr= Received power of the transmitter at distance d
Pt= Power transmitted by the transmitter
Gt= Gain of the transmitter
Gr= Gain of the receiver
Ht= Height of the transmitter
Hr= Height of the receiver
Lr= Receiver cable loss
Lpol=System loss due to polarization
D= separation distance between transmitter and receiver
iv. Shadowing Model
This model considers logarithmic relationship between transmitted power and received power at a certain
distance. It involves a normalized random variable which accounts for path loss in different environment.
Power received at distance d can be computed by considering relationship with received power at reference
distance d0 as shown in the following equation:
0
0d d
dP P
d
σ
=
(11)
In decibel
0 1 01 0 lo g ( )0
d d
dP P
dσ= +
(12)
Where;
Pd= Power received at distance d
Pd0= Power received at reference distance d0
σ = path loss exponent
For this paper Free Space model have been considered
Some typical values of path loss exponent are shown in table 3
Journal of Information Engineering and Applications www.iiste.org
ISSN 2224-5782 (print) ISSN 2225-0506 (online)
Vol.4, No.12, 2014
14
Table 3: Path loss exponent values for different environment
Environment Path loss Exponent Value
Free Space 2
Shadowed urban 3-5
Urban Area Cellular radio 2.7-3.5
In building line of sight 1.6-1.8
Obstructed in building 4-6
Obstructed in factories 2-3
3. Materials and Methods
Field measurements were conducted in Arusha and Iringa town and data collection exercise involved
measurement of electric field strength and power levels from all broadcasting radio stations in Arusha and Iringa.
Comparison between measured data and minimum thresholds levels were conducted for those stations which
were located in the same transmission tower and their out of band emission was found to be present in
aeronautical frequency.
i. Transmission Site
In Arusha broadcasting stations have installed their transmitters at the themi hill site, height of transmission
tower was found to be 62 metre and the tower is located at Latitude 03º22ˈ33.38ˈˈ Longitude 36º40ˈ39.26ˈˈ
Altitude 1365. Aeronautical ground to air communication facilities use 118.4 MHz frequency and have been
installed at the control tower of Arusha airport which is located at latitude 03º22ˈ06ˈS and longitude
36º37ˈ29.40ˈˈ this area at altitude of 1361 m above sea level and Electric field strength of COM system
measured was 91.77 dBµV.
Parameters for two broadcasting stations in Arusha town which were found to have out of band
emission in COM frequency were as stipulated in Table 3
Table 4: Transmission parameters for 105.7 MHz and 93.0 MHz broadcasting stations
Parameter Station1 Station 2
Transmitter Power 1000 W 1000 W
Transmitter Frequency 105.7 MHz 93.0 MHz
Transmitting Antenna Gain 8.5 dBi 6 dBi
Antenna Type Dipole Dipole
Cable Loss 0.2 dB 0.2 dB
Tower Height 62 m 62 m
Figure1: 105.7MHz Transmitter
Journal of Information Engineering and Applications www.iiste.org
ISSN 2224-5782 (print) ISSN 2225-0506 (online)
Vol.4, No.12, 2014
15
Figure 2: 93.0 MHz Transmitter
In Iringa FM broadcasting radio stations were located at Nyamafifi hill situated at 7˚45'50.72'' S,
35˚42'58.55'' E, Altitude: 1,769m above mean sea level
iii. Measurement Devices
For electric field strength measurement Rhode and Schwarz Spectrum Analyser was used while spatial
information was collected by from ROMES software which has GPS Receiver attachment.
Figure 3: Spectrum Analyser
Journal of Information Engineering and Applications www.iiste.org
ISSN 2224-5782 (print) ISSN 2225-0506 (online)
Vol.4, No.12, 2014
16
Figure 4: Monitoring Vehicle
iv. Measurement Routes
Three different routes were selected for measurement exercise in Arusha town include;
Route 1 from themi hill to njiro road passing nanenane, and tanesco,
Route 2 from themi hill to kisongo passing along sokoine road and Arusha airport
Route 3 from themi hill to moshono passing maasai camp
These routes were selected based on environment
4. Results and Analysis
4.1 Source of interference in Arusha
Field measurements depict intermodulation products from FM broadcasting radio stations to be the source of
interference to COM systems
In Arusha interfered aeronautical frequency was 118.4 MHz by using spectrum analyser interfering
signal level was observed to be above minimum threshold level of -102dBm. Further analysis of observed
signals showed there was third order intermodulation product relationship which is given by
(13)
Where f1>f2
f1= 105.7MHz, f2= 93.0 MHz
4.2 Sources of interference in Iringa
For the case of Iringa interference, interfered frequency was 118.1 MHz, analysis of interference shows that
three FM broadcasting radio station intermodulation and produce effect in aeronautical frequency.
1 2 3I M f f f= + −
(14)
Where
f1>f2>f3
f1= 104.9 MHz, f2= 103.6MHz, f3= 90.4MHz
4.3 Simulation Result
Matlab simulation of measured received power levels data against empirical path loss models for two radios in
Arusha are shown in figure 1 and figure 2
The comparison between the observed and predicted path loss models has been done by using
Normalized Mean Mean Square Error and show that Egli model can be used to predict power level of
broadcasting FM stations.
Journal of Information Engineering and Applications www.iiste.org
ISSN 2224-5782 (print) ISSN 2225-0506 (online)
Vol.4, No.12, 2014
17
0 1 2 3 4 5 6 7 8 9-80
-70
-60
-50
-40
-30
-20
-10
0
Line of Sight Distance (km)
Re
ce
ive
d P
ow
er
lev
el
(dB
m)
Two Ray Model
Free Space Model
Measured (105.7 MHz)
Egli Model
Figure 5: Received Power level (dBm) from 105.7 MHz vs Line of Sight Distance (Km)
0 1 2 3 4 5 6 7 8 9-80
-70
-60
-50
-40
-30
-20
-10
0
Line of Sight Distance (km)
Re
ce
ive
d P
ow
er
lev
el
(dB
m)
Two Ray Model
Free Space Model
Measured(93.0 MHz)
Egli Model
Figure 6: Receive Power Level (dBm) from 93 MHz Radio vs Line of Sight Distance
Journal of Information Engineering and Applications www.iiste.org
ISSN 2224-5782 (print) ISSN 2225-0506 (online)
Vol.4, No.12, 2014
18
F93.0 F105.70
5
10
15
20
25
30
35
40Normalized Root Mean Square(%)
Egli
Two Ray
Free Space
Figure 7: Normalized Root Mean Square
5. Conclusion
This paper has focused on comparing measured level of FM broadcasting signal reaching COM facilities with
established protection ratios. The minimum threshold levels established by ICAO and those of FCC result show
that the level of signal was above recommended standard hence pose a need for interference mitigation technique
which will facilitate in lowering FM broadcasting radios signal power level reaching aeronautical facilities.
Future work to be done in order to mitigate interference is design of Corner reflector antenna due to its
good front to back radiation pattern which is the ratio of the maximum directivity of an antenna to its directivity
in the rearward direction which will reduce FM broadcasting signal level in direction of aeronautical ground to
air VHF facilities.
Acknowledgement
We wish to extend our appreciation to the Nelson Mandela African Institute of Science and Technology
(NMAIST) and the School of Computation and Communication Science and Engineering (CoCSE) for
supporting this work and for granting their resources.
References
[1] S. A. Jan Kaaya, "REVIEW ON ELECTROMAGNETIC INTERFERENCE AND COMPATIBILITY
IN AERONATICAL RADIOCOMMUNICATION SYSTEMS –TANZANIA CASE STUDY. ," 2014.
[2] V. P. Kodali. (1996). Engineering Electromagnetic Compatibility Principles, Measurements and
Technologies.
[3] ITU, "Compatibility between the sound-broadcasting service in the band of about 87-108 MHz and the
aeronautical services in the band 108-137 MHz," Recommendation ITU-R SM.1009-1, 1995.
[4] R. Womersley, "Investigation of interference sources and mechanisms for Eurocontrol," Smith System
Engineering Limited (Smith), 1997.
[5] W. Radio Technical Commission for Aeronautics, DC, USA., " Minimum operational performance
standards for airborne ILS localizer receiving equipment operating within the radio frequency range of
108-112 MHz. ," 1986.
[6] R. I.-R. SM.2021, "PRODUCTION AND MITIGATION OF INTERMODULATION PRODUCTS IN
THE TRANSMITTER," 2000.
[7] ICAO. (2012). HANDBOOK ON RADIO FREQUENCY SPECTRUM REQUIREMENTS FOR
CIVIL AVIATION: PART II FREQUENCY ASSIGNMENT PLANNING CRITERIA FOR
Journal of Information Engineering and Applications www.iiste.org
ISSN 2224-5782 (print) ISSN 2225-0506 (online)
Vol.4, No.12, 2014
19
AERONAUTICAL COMMUNICATION AND NAVIGATION SYSTEMS.
[8] ICAO, "HANDBOOK ON RADIO FREQUENCY SPECTRUM REQUIREMENTS FOR CIVIL
AVIATION: PART II FREQUENCY ASSIGNMENT PLANNING CRITERIA FOR
AERONAUTICAL COMMUNICATION AND NAVIGATION SYSTEMS," 2012.
[9] J. S. Seybold, Introduction to RF Propagation. Wiley Interscience, 2005.
[10] A. G. L. a. P. L. Rice, "Prediction of tropospheric radio transmission loss over irregular terrain a
computer method. ," NTIA 1968.
[11] S. Hurley, "Planning Effective Cellular Mobile Radio Networks," IEEE TRANSACTIONS ON
VEHICULAR TECHNOLOGY, vol. 51, 2002.
[12] P. K. Pardeep Pathania, Shashi B. Rana, "Performance Evaluation of different Path Loss Models for
Broadcasting applications," American Journal of Engineering Research (AJER), 2014.
[13] O. Y. O. Famoriji John Oluwole, "Radio Frequency Propagation Mechanisms and Empirical Models for
Hilly Areas," International Journal of Electrical and Computer Engineering (IJECE), vol. 3, 2013.
[14] P. D. Vishwantah, "Radio frequency channel modeling for proximity networks on the Martian,"
Elsevier, 2004.
[15] T. S. Rappaport, "Wireless Communications, Principles and Practice ." 2002.
The IISTE is a pioneer in the Open-Access hosting service and academic event management.
The aim of the firm is Accelerating Global Knowledge Sharing.
More information about the firm can be found on the homepage:
http://www.iiste.org
CALL FOR JOURNAL PAPERS
There are more than 30 peer-reviewed academic journals hosted under the hosting platform.
Prospective authors of journals can find the submission instruction on the following
page: http://www.iiste.org/journals/ All the journals articles are available online to the
readers all over the world without financial, legal, or technical barriers other than those
inseparable from gaining access to the internet itself. Paper version of the journals is also
available upon request of readers and authors.
MORE RESOURCES
Book publication information: http://www.iiste.org/book/
Academic conference: http://www.iiste.org/conference/upcoming-conferences-call-for-paper/
IISTE Knowledge Sharing Partners
EBSCO, Index Copernicus, Ulrich's Periodicals Directory, JournalTOCS, PKP Open
Archives Harvester, Bielefeld Academic Search Engine, Elektronische Zeitschriftenbibliothek
EZB, Open J-Gate, OCLC WorldCat, Universe Digtial Library , NewJour, Google Scholar